Deadlock might happens when database is shutting down with internal worker attachments exists.

[hvlad]

Deadlock between WorkerAttachment::shutdownDbb() and WorkerStableAttachment::doOnIdleTimer() due to wrong mutexes lock order, see stacks below:

One thread enters m_mapMutex (by WorkerAttachment::shutdownDbb()) and waits for StableAttachmentPart::mainSync:

engine13.dll!Firebird::Mutex::enter(const char * aReason=0x00007ff9c779e140) Line 95
	at src\common\classes\locks.h(95)
engine13.dll!Jrd::StableAttachmentPart::Sync::enter(const char * aReason=0x00007ff9c779e140) Line 231
	at src\jrd\Attachment.h(231)
engine13.dll!Firebird::RaiiLockGuard<Jrd::StableAttachmentPart::Sync>::RaiiLockGuard<Jrd::StableAttachmentPart::Sync>(Jrd::StableAttachmentPart::Sync & aLock={...}, const char * aReason=0x00007ff9c779e140) Line 331
	at src\common\classes\locks.h(331)
engine13.dll!Jrd::WorkerStableAttachment::fini() Line 113
	at src\jrd\WorkerAttachment.cpp(113)
engine13.dll!Jrd::WorkerAttachment::doDetach(Firebird::CheckStatusWrapper * status=0x000000000014df78, Jrd::StableAttachmentPart * sAtt=0x0000000004593110) Line 475
	at src\jrd\WorkerAttachment.cpp(475)
engine13.dll!Jrd::WorkerAttachment::clear(bool checkRefs=false) Line 402
	at src\jrd\WorkerAttachment.cpp(402)
engine13.dll!Jrd::WorkerAttachment::shutdownDbb(Jrd::Database * dbb=0x00000000008052d0) Line 241
	at src\jrd\WorkerAttachment.cpp(241)
engine13.dll!JRD_shutdown_database(Jrd::Database * dbb=0x00000000008052d0, const unsigned int flags=3) Line 7963
	at src\jrd\jrd.cpp(7963)
engine13.dll!purge_attachment(Jrd::thread_db * tdbb=0x000000000014eb80, Jrd::StableAttachmentPart * sAtt=0x000000000429f9a0, unsigned int flags=2) Line 8449
	at src\jrd\jrd.cpp(8449)
engine13.dll!Jrd::JAttachment::freeEngineData(Firebird::CheckStatusWrapper * user_status=0x000000000014ee58, bool forceFree=false) Line 3349
	at src\jrd\jrd.cpp(3349)
engine13.dll!Jrd::JAttachment::internalDetach(Firebird::CheckStatusWrapper * user_status=0x000000000014ee58) Line 3286
	at src\jrd\jrd.cpp(3286)
engine13.dll!Jrd::JAttachment::detach(Firebird::CheckStatusWrapper * user_status=0x000000000014ee58) Line 3298
	at src\jrd\jrd.cpp(3298)

Another thread enters StableAttachmentPart::mainSync (by WorkerAttachment::detachIdle) and waits for m_mapMutex:

engine13.dll!Firebird::Mutex::enter(const char * aReason=0x00007ff9c779e170) Line 95
	at src\common\classes\locks.h(95)
engine13.dll!Firebird::RaiiLockGuard<Firebird::Mutex>::RaiiLockGuard<Firebird::Mutex>(Firebird::Mutex & aLock={...}, const char * aReason=0x00007ff9c779e170) Line 331
	at src\common\classes\locks.h(331)
engine13.dll!Jrd::WorkerAttachment::getByName(const Firebird::StringBase<Firebird::PathNameComparator> & dbname={...}) Line 188
	at src\jrd\WorkerAttachment.cpp(188)
engine13.dll!Jrd::WorkerAttachment::detachIdle(Jrd::StableAttachmentPart * sAtt=0x0000000004593110) Line 416
	at src\jrd\WorkerAttachment.cpp(416)
engine13.dll!Jrd::WorkerStableAttachment::doOnIdleTimer(Firebird::TimerImpl * timer=0x0000000004593b30) Line 106
	at src\jrd\WorkerAttachment.cpp(106)
engine13.dll!Jrd::StableAttachmentPart::onIdleTimer(Firebird::TimerImpl * timer=0x0000000004593b30) Line 377
	at src\jrd\Attachment.h(377)
[External Code]
engine13.dll!Firebird::TimerImpl::handler() Line 64
	at src\common\classes\TimerImpl.cpp(64)
engine13.dll!Firebird::ITimerBaseImpl<Firebird::TimerImpl,Firebird::CheckStatusWrapper,Firebird::IReferenceCountedImpl<Firebird::TimerImpl,Firebird::CheckStatusWrapper,Firebird::Inherit<Firebird::IVersionedImpl<Firebird::TimerImpl,Firebird::CheckStatusWrapper,Firebird::Inherit<Firebird::ITimer>>>>>::cloophandlerDispatcher(Firebird::ITimer * self=0x0000000004593b38) Line 15722
	at src\include\firebird\IdlFbInterfaces.h(15722)
fbclient.dll!Firebird::ITimer::handler() Line 4553
	at src\include\firebird\IdlFbInterfaces.h(4553)
fbclient.dll!Why::`anonymous namespace'::TimerEntry::timeThread(void * __formal=0x0000000000000000) Line 286
	at src\yvalve\MasterImplementation.cpp(286)
fbclient.dll!`anonymous namespace'::ThreadArgs::run() Line 78
	at src\common\ThreadStart.cpp(78)

Only SuperServer is affected.